Process for the preparation of a nitrophosphate fertilizer

ABSTRACT

A process for the preparation of nitrophosphate fertilizer by acidulation of phosphate rock by means of a mixture of HNO3 and NH4HSO4, wherein the NH4HSO4, serves for the acidulation as well as for the precipitation of the calcium present in the phosphate rock as CaSO4.2H2O. The latter is treated with a gas mixture containing NH3 and CO2, forming CaCO3 and (NH4)2SO4. The (NH4)2SO4 is thermally decomposed to form NH4HSO4, which is recycled to the acidulation reaction. The acidulated phosphate rock solution is neutralized with NH3 to obtain the nitrophosphate fertilizer.

United States Patent Guery [451 Apr. 4, 1972 [54] PROCESS FOR THEPREPARATION OF A NITROPHOSPHATE FERTILIZER [21] Appl. No.: 882,603

[30] Foreign Application Priority Data FOREIGN PATENTS OR APPLICATIONS810,208 3/1959 Great Britain ..71/34 1,153,037 8/1963 Germany ..71/37OTHER PUBLICATIONS Mellor, A Comprehensive Treatise On inorganic &Theoreti cal Chemistry, Vol. 2, 1922, pages 702- 705, Longmans, Green &Co., New York.

Primary Examiner-Rueben Friedman Assistant Examiner-Bennett l-l.Levenson Dec. 18, 1968 Netherlands..........,. ,81&64 A"0mey Kun Kelman[52] U.S. Cl ..71/35, 23/66, 71/37, 57 ABSTRACT 71/39, 71/63 [51] Int.Cl. ..C05b 11/06 I A Process for the Preparanon of mtmphosphzfte femhze'by 58 F1 Id rsea h ..71 39, 35, 37, 63; 23 119 acidulafiml PlwsPhate bymeans fHNO5 1 e N I l and Nn,nso,, wherein the muse, serves for theacidula- 56 R I e Cit d tion as well as for the precipitation of thecalcium present in l 1 e H aces e the phosphate rock as CaSO -2H O. Thelatter is treated with UNITED STATES PATENTS a gas mixture containingNH; and CO forming CaCO and (NI-1.0 50. The (NI-1.0 80 is thermallydecomposed to form 1,517,687 12/1924 Voerkehus ..71/39 NHHSO" i h irecycled to the acidulation reaction The 1,758,448 5/1930 Lil enroth..71/39 X acidulated phosphate rock solution is neutralized with NHa tol ,902,649 3/1933 Larsson ..23/1 19 obtain the nitrophosphate fertilizeL2,795,486 6/1957 P1uim..... ...23/l19 3,172,751 3/1965 Datm ..71/37 2Claims, 1 Drawing Figure PHaJP/IHTE 05K mvo 41 fi/PFUM COIVI5IOAI Y(0.5% /V// +60 flz'lflacflr/ofl 4 (05% *[0[% Q7 4 I STEAM /4 near/omfgffl (676% [0 F74 7897/? /V// i Z l 4/511 7244/2470 04 #07- Fw; 6455snun/ale, V p;7rm%:jfla

St/fiEEl/EflTED $277M [0,

Patented April 4, 1972 new mRRkQQQlQ ARIEH Y. 6027!) BY 7 Man PROCESSFOR THE PREPARATION OF A NITROPHOSPHATE FERTILIZER The present inventionis concerned with a process for the preparation of a nitrophosphatefertilizer.

In the proposed process, the amount of nitric acid required for thedissolution of a given kind of phosphate rock is about half of that usedin known nitrophosphate processes, resulting in a fertilizer with aproportionally lower nitrogen to phosphorus pentoxide ratio. In currentpractice, calcium nitrate produced in the dissolution of phosphate rockin nitric acid is either separated by low temperature crystallization orreacted with ammonium sulphate, resulting in the precipitation of gypsumand the production of an equivalent amount of ammonium nitrate.

The acidulation of phosphate rock in conventional nitrophosphateproduction involving precipitation of gypsum can be presented asfollows:

Gypsum is filtered off and converted to ammonium sulphate by reactionwith ammonia and CO Ammonium sulphate produced is recycled toreaction 1. The filtrate is neutralized I to yield nitrophosphatefertilizer.

Acid ammonium sulphate NH HSO along with the required,

amount of nitric acid, is used for the acidulation of phosphate rock inwhich the acid sulphate replaces an equivalent amount of nitric acid.

The process of the invention is illustrated in the flow sheet of theaccompanying drawing illustrating the sequence of reaction steps.

As shown in the flow sheet by the legends, phosphate rock is acidulatedwith a mixture of l-lNO: and NH HSO while the acid ammonium sulphatesimultaneously precipitates calcium present in the phosphate rock toobtain CaSO,,. The calcium sulphate is separated and treated with NH;,and CO to obtain CaCO and (Ni- 50 The calcium carbonate is removed andthe recovered ammonium sulphate crystals are thermally decomposed. Theammonium sulphate crystals are first heated to a temperature at whichdecomposition starts whereby evolution of ammonia commences and anammonium sulphate containing melt of acid ammonium sulphate is obtained.The'temperature of the melt is then raised and the melt is contactedcountercurrently with a stream of hot stripping gas containing CO inadmixture with superheated steam and/or hot flue gases freed of oxygenuntil a melt containing more than 90 percent NH HSO is obtained. The CO,and evolved Nl-l including the hot flue gases and/or superheated steamare passed back to the gypsum conversion while the acid ammoniumsulphate is recycled to the phosphate rock acidulation step. After theseparation of calcium sulphate, the acidulated phosphate rock solutionis neutralized with ammonia to obtain the nitrphosphate fertilizer.

A. ACIDULATION C8[0F2(PO4)5 aqu. sol.

It can be seen from reaction 2 that, in the proposed process, the ratioof N P 0 is half of that obtained in the conventional process (Reaction1). in case the acid ammonium sulphate in Reaction 2 contains someundissociated ammonium sulphate and as result thereof has too low anacidity, this shortage is made up by addition of an equivalent amount ofnitric acid.

B. NEUTRALIZATION After filtration of CaSO 2l-l O, the filtrate obtainedin Reaction 2 containing free H PO HF and ammonium nitrate, isneutralized by ammonia to yield nitrophosphate fertilizer. C. RECOVERYOF ACID AMMONIUM SULPHATE The gypsum precipitated in reaction 2 is firstconverted to ammonium sulphate by reaction with ammonia and carbondioxide.

aqu. sol.

C3804 ZHgO 2NH CO2 4)2S04 CaCO H 0 Precipitated calcium carbonate isfiltered off. Ammonium sulphate crystals are recovered from thefiltrate. The ammonium sulphate crystals are then subjected to atemperature above 300C, causing decomposition into the acid salt andfree ammonia according to the following reaction:

possible and to obtain a mixture with more than 90 percent NH HSO themelt is heated to about 400C. and contacted in countercurrent with astream of a hot stripping gas in a suitable contacting device like apacked column or a spraying tower. It is advantageous to use for thisstripping the relatively pure CO which is used for the gypsumconversion, in a mixture with hot flue gases and/or superheated steam,after which the mixture containing CO and NH; along with the hot fluegases and/or superheated steam is passed to the gypsum conversionreactor for forming ammonium sulphate and preparing calcium carbonate.The hot flue gases may be freed from oxygen by passing through a bed ofred-hot coke, before being mixed with relatively pure CO NHJ'ISQ, isrecycled to the phosphate rock acidulation reaction while free NH; isreturned to the gypsum to ammonium sulphate conversion step.

Since ammonium sulphate has to be in solid form for its conversion tothe acid salt, and in order to minimize the need for evaporation ofammonium sulphate solution, the reaction of NH;, and CO with gypsum maybe carried out in a known manner in a reaction liquor saturated withammonium sulphate, containing calcium carbonate and ammonium sulphatecrystals in suspension, to produce ammonium sulphate and calciumcarbonate crystals directly. The latter can be separated by making useof their difference in specific gravity or in particle size.

If, for example, this separation is carried out in a hydrocyclone,heavier ammonium sulphate crystals will be received from the bottomfraction and lighter calcium carbonate crystals from the overheadstream.

Some ammonium sulphate, possibly carried along in the calcium carbonatefraction may be effectively used, by using the calcium carbonate withthe ammonium sulphate impurity for the preparation of nitrolimefertilizer.

I claim:

1. A process for the preparation of a nitrophosphate fertilizer fromphosphate rock, comprising the steps of l. acidulating the phosphaterock with a mixture of HNO},

and NH HSO 2. simultaneously precipitating calcium present in thephosphate rock with the Nl-LHSO, to obtain CaSO and separating the CaSO3. treating the separated CaSO with a gas mixture containing CO and NHto obtain CaCO and (NI-M 50 4. removing the CaCO by filtration, andrecovering (NI-l SOB4 crystals from the filtrate,

5. thermally decomposing the (NI- Q by a. the (NI-M 80 at a temperatureat g to p for icbrnvel'tring 504 t6 C C and decomposition thereofstarts, thereby evolving am- 02 4,whi h p p m pmhflfl monia, and untilan (NH,),SO containing melt of the recovered (NHA)2SO4 15 recycled to pf! ifl Qt srqbtaiasd, and. m V V. A V 4'9292795192 tQEMiSQQh W V r b.raising the temperature of the melt to about 400C. and ree elingtl estep) to step and contacfing the melt f 'f f y i a smiam of 8.neutralizing the acidulated phosphate rock solution, after hot strippinggas containing CO in admixture with suthe separation of the Casopursuant to step (2) with perheated steam and/or hot flue gases freedfrom ox- NH3 to obtain the nitmphosphac fertilize ygen, until a meltcontaining more than 90 percent NHHSO4 is obtained [0 2. :Ihe process ofclaim 1, wherein the temperature at step 6. passing the stripping gasmixture resulting from step (5), (510151" range of at least 160 200containing CO and lflll; along withthestearnanrl/or flue it im s

2. simultaneously precipitating calcium present in the phosphate rockwith the NH4HSO4 to obtain CaSO4, and separating the CaSO4,
 2. Theprocess of claim 1, wherein the temperature at step (5a) is in the rangeof at least 160* to 200*C.
 3. treating the separated CaSO4 with a gasmixture containing CO2 and NH3 to obtain CaCO3 and (NH4)2SO4, 4.removing the CaCO3 by filtration, and recovering (NH4)2SO4 crystals fromthe filtrate,
 5. thermally decomposing the (NH4)2SO4 by a. heating the(NH4)2SO4 at a temperature at which decomposition thereof starts,thereby evolving ammonia, and until an (NH4)2SO4 containing melt ofNH4HSO4 is obtained, and b. raising the temperature of the melt to about400*C. and contacting the melt countercurrently with a stream of hotstripping gas containing CO2 in admixture with superheated steam and/orhot flue gases freed from oxygen, until a melt containing more than 90percent NH4HSO4 is obtained,
 6. passing the stripping gas mixtureresulting from step (5), containing CO2 and NH3 along with the steamand/or flue gases, to step (3) for converting CaSO4 to CaCO3 and(NH4)2SO4, which are separated pursuant to step (4), and the recovered(NH4)2SO4 is recycled to step (5) for reconversion to NH4HSO4, 7.recycling the NH4HSO4 from step (6) to step (1), and
 8. neutralizing theacidulated phosphate rock solution, after the separation of the CaSO4pursuant to step (2), with NH3 to obtain the nitrophosphate fertilizer.